Field of the Invention
The present invention relates to a data communication technique.
Description of the Related Art
In order to perform bidirectional communication between a control apparatus that serves as a master and a data processing apparatus that serves as a slave, for example, a two-wire communication interface is used. Japanese Patent No. 4393351 and Japanese Patent Laid-Open No. 2014-121015 disclose communication systems that perform communication by using a two-wire communication interface, wherein data transmission and reception, power supply, and supply of synchronization signals are performed using two signal lines. In the configuration disclosed in Japanese Patent No. 4393351, the control apparatus outputs a pulse signal to a first terminal and a reference voltage to a second terminal. Here, power is supplied from the control apparatus to the data processing apparatus by using a voltage difference between the first terminal and the second terminal. Also, the pulse signal is a synchronization signal, and the data processing apparatus generates a synchronization timing based on the pulse signal. Furthermore, the control apparatus transmits data “0” and data “1” based on the duty ratio of the pulse signal, and the data processing apparatus transmits data “0” and data “1” based on the level of electric current that flows between the terminals. In order to increase the communication speed in the configuration disclosed in Japanese Patent No. 4393351, it is necessary to increase the frequency of the pulse signal.
However, due to the characteristics of a driving circuit that generates the pulse signal, the rising edge and the falling edge of the pulse signal are rounded, and thus there is a limit to increasing the frequency of the pulse signal. Accordingly, there is a demand for increasing the transmission rate, in particular, the transmission rate from the data processing apparatus to the control apparatus, without increasing the frequency of the pulse signal.
Also, according to Japanese Patent Laid-Open No. 2014-121015, the control apparatus sets the pulse signal to a high level so as to cause the data processing apparatus to transmit data. Then, the data processing apparatus transmits data to the control apparatus by increasing or decreasing the electric current that flows through a line according to a data value while the pulse signal from the control apparatus is at a high level. The control apparatus identifies the data from the data processing apparatus at a predetermined timing relative to the rising timing of the pulse signal. Here, there is a delay time td from when the control apparatus sets the pulse signal to a high level so as to cause the data processing apparatus to transmit data to when the control apparatus receives the data transmitted by the data processing apparatus. Accordingly, the control apparatus starts reading data (data value identification) after, for example, the delay time td has passed after setting the pulse signal to a high level.
However, the delay time td varies according to the environment and individual difference between apparatuses. For this reason, the control apparatus needs to have a sufficient margin for the variation of the delay time td when reading data. This increases the time required for data communication.